Physlib

PhyslibAlpha.AlgebraicFramework.OrderUnit.Symmetry

Symmetry: order-automorphisms and their action on states

i. Overview

Physically, a symmetry of a system is a *reversible* transformation: a change of description that loses no information and can always be undone. In the order-unit picture (`Channel/Basic.lean`) a transformation between effect algebras is a channel, a unital positive linear map; a symmetry is exactly a channel `φ : E →ₚ₁[ℝ] E` that is invertible with an inverse `φ⁻¹` that is *also* a channel. Both directions have to be physical: undoing a symmetry must again be positive and send the certain event to the certain event, not just be some linear inverse.

A group `G` acting on `E` "by symmetries" is then a homomorphism `ρ : G →* Symmetry E` into the group of such automorphisms. Every symmetry, via `UnitalPositiveLinearMap.comp`, transports a state: precomposing a state `ω : E →ₚ₁[ℝ] ℝ` with `φ⁻¹` gives the state that assigns to an observable `x` whatever `ω` assigned to the pulled-back observable `φ⁻¹ x`. This needs no new proof of positivity or normalization — `ω.comp φ⁻¹` is already a unital positive linear map because `.comp` always is; all that is new here is checking this assignment is a genuine group action, `(g*h) • ω = g • (h • ω)` and `1 • ω = ω`, which reduces to associativity and identity laws for `.comp` already on hand.

This is the state-level pushforward along a channel, specialized to a channel that happens to be invertible (`Channel/Basic.lean`'s `Weight.comp` is the same idea one level down, on weights on the positive cone; working with the state directly as a `UnitalPositiveLinearMap` avoids the extra order-unit hypotheses `Weight.comp` needs and is the cleaner route here).

ii. Key definitions and results

- `IsOrderAutomorphism φ`: `φ` is a channel with a two-sided inverse that is also a channel. - `Symmetry E`: the bundled group of order-automorphisms of `E`, with `Group` instance `mul := comp`. - The `MulAction (Symmetry E) (𝓢[ℝ, E])` instance: pushing a state forward along the inverse automorphism. - `stateSMul`: the action of a general `G` on `𝓢[ℝ, E]` induced by a homomorphism `ρ : G →* Symmetry E`, together with the group action laws it satisfies. - `OneParameterAutomorphismGroup E`: a one-parameter (reversible dynamics) family `α : ℝ → (E →ₚ₁[ℝ] E)` with `α 0 = id` and `α (s + t) = α s ∘ α t`, each `α t` an automorphism.

iii. Table of contents

  • A. Order automorphisms
  • B. The symmetry group
  • C. The induced action on states
  • D. One-parameter automorphism groups

A. Order automorphisms

B. The symmetry group

C. The induced action on states

D. One-parameter automorphism groups: reversible dynamics

33 declarations

definition

ϕ\phi is an order-automorphism

A unital positive linear map (also called a channel) ϕ:E→E\phi : E \to E is an order-automorphism if there exists another unital positive linear map ψ:E→E\psi : E \to E such that ψ∘ϕ=idE\psi \circ \phi = \text{id}_E and ϕ∘ψ=idE\phi \circ \psi = \text{id}_E. This implies that ϕ\phi is a reversible transformation where both the map and its inverse preserve the order and the unit of the space EE.

theorem

The identity map is an order-automorphism

The identity map idE:E→E\text{id}_E: E \to E is an order-automorphism.

definition

Inverse of an order-automorphism ϕ\phi

Given a unital positive linear map ϕ:E→E\phi : E \to E (also referred to as a channel) and a proof hh that ϕ\phi is an order-automorphism, this definition provides the inverse unital positive linear map ϕ−1:E→E\phi^{-1} : E \to E. This inverse map satisfies the conditions ϕ−1∘ϕ=idE\phi^{-1} \circ \phi = \text{id}_E and ϕ∘ϕ−1=idE\phi \circ \phi^{-1} = \text{id}_E, ensuring that the reversal of the transformation is itself a valid channel (i.e., it preserves both the order and the unit of the space EE).

theorem

ϕ−1∘ϕ=idE\phi^{-1} \circ \phi = \text{id}_E for an order-automorphism ϕ\phi

Let ϕ:E→E\phi : E \to E be a unital positive linear map that is an order-automorphism, and let ϕ−1\phi^{-1} be its inverse. Then the composition of ϕ−1\phi^{-1} and ϕ\phi is the identity map on EE, written as ϕ−1∘ϕ=idE\phi^{-1} \circ \phi = \text{id}_E.

theorem

ϕ∘ϕ−1=idE\phi \circ \phi^{-1} = \text{id}_E for an Order-Automorphism ϕ\phi

Let EE be a space and ϕ:E→E\phi : E \to E be a unital positive linear map (a channel). If ϕ\phi is an order-automorphism, let ϕ−1\phi^{-1} denote its inverse unital positive linear map. Then the composition of ϕ\phi with its inverse is the identity map on EE, denoted as ϕ∘ϕ−1=idE\phi \circ \phi^{-1} = \text{id}_E.

theorem

ϕ−1(ϕ(x))=x\phi^{-1}(\phi(x)) = x for an order-automorphism ϕ\phi

Let ϕ:E→E\phi : E \to E be a unital positive linear map (a channel) on an order-unit space EE. If ϕ\phi is an order-automorphism with inverse ϕ−1\phi^{-1}, then for any x∈Ex \in E, applying ϕ\phi followed by ϕ−1\phi^{-1} returns the original element: ϕ−1(ϕ(x))=x\phi^{-1}(\phi(x)) = x

theorem

ϕ(ϕ−1(x))=x\phi(\phi^{-1}(x)) = x for order-automorphisms

Let ϕ:E→E\phi: E \to E be an order-automorphism (a unital positive linear map with a unital positive linear inverse ϕ−1\phi^{-1}). For any element x∈Ex \in E, applying the inverse map followed by the map ϕ\phi returns the original element: ϕ(ϕ−1(x))=x\phi(\phi^{-1}(x)) = x

theorem

The inverse of an order-automorphism is an order-automorphism

Let EE be an order-unit space and ϕ:E→E\phi : E \to E be a unital positive linear map. If ϕ\phi is an order-automorphism, then its inverse ϕ−1\phi^{-1} is also an order-automorphism.

theorem

The composition of two order-automorphisms is an order-automorphism

Let EE be a space and ϕ,ψ:E→E\phi, \psi: E \to E be unital positive linear maps (channels). If ϕ\phi and ψ\psi are order-automorphisms, then their composition ϕ∘ψ\phi \circ \psi is also an order-automorphism.

theorem

An order-automorphism is bijective

Let EE be an order-unit space (a real ordered vector space with a distinguished unit element) and let ϕ:E→E\phi : E \to E be a unital positive linear map. If ϕ\phi is an order-automorphism, then ϕ\phi is a bijective function.

abbrev

Symmetry of EE

Let EE be a real vector space equipped with a partial order and a unit element 11. The type `Symmetry E` is the set of all unital positive linear maps ϕ:E→E\phi: E \to E (also known as channels) that are order-automorphisms. A map ϕ\phi is an order-automorphism if there exists an inverse unital positive linear map ϕ−1\phi^{-1} such that ϕ∘ϕ−1=idE\phi \circ \phi^{-1} = \text{id}_E and ϕ−1∘ϕ=idE\phi^{-1} \circ \phi = \text{id}_E. This structure bundles the map with the proof that it and its inverse preserve both the ordering and the unit of EE.

theorem

Extensionality of symmetries: ϕ(x)=ψ(x)  ⟹  ϕ=ψ\phi(x) = \psi(x) \implies \phi = \psi

Let EE be a real vector space equipped with a partial order and a unit element. If ϕ\phi and ψ\psi are symmetries of EE (unital positive linear maps that are order-automorphisms) such that ϕ(x)=ψ(x)\phi(x) = \psi(x) holds for every x∈Ex \in E, then ϕ=ψ\phi = \psi.

instance

Identity element of Symmetry E\text{Symmetry } E

The identity element 11 for the group of symmetries Symmetry E\text{Symmetry } E is defined as the identity unital positive linear map idE:E→E\text{id}_E : E \to E.

instance

Multiplication in Symmetry E\text{Symmetry } E as composition ϕ∘ψ\phi \circ \psi

Given two symmetries ϕ,ψ∈Symmetry E\phi, \psi \in \text{Symmetry } E of a real ordered vector space with unit EE, their multiplication ϕ⋅ψ\phi \cdot \psi is defined as the composition of the underlying unital positive linear maps ϕ∘ψ\phi \circ \psi. This composition results in a new order-automorphism of EE.

instance

Inverse of a symmetry ϕ∈Symmetry E\phi \in \text{Symmetry } E

This definition provides the inverse operation for the group of symmetries of EE. For any symmetry ϕ∈Symmetry E\phi \in \text{Symmetry } E, its inverse ϕ−1\phi^{-1} is the symmetry whose underlying map is the inverse unital positive linear map (channel) satisfying ϕ∘ϕ−1=idE\phi \circ \phi^{-1} = \text{id}_E and ϕ−1∘ϕ=idE\phi^{-1} \circ \phi = \text{id}_E.

theorem

The identity of Symmetry E\text{Symmetry } E is idE\text{id}_E

Let EE be a real ordered vector space with unit. The underlying unital positive linear map of the identity element 11 in the group of symmetries Symmetry E\text{Symmetry } E is the identity map idE\text{id}_E on EE.

theorem

The underlying map of ϕ⋅ψ\phi \cdot \psi is ϕ∘ψ\phi \circ \psi

Let EE be a real ordered vector space with a unit. For any two symmetries ϕ,ψ∈Symmetry E\phi, \psi \in \text{Symmetry } E, the underlying unital positive linear map (channel) of their product ϕ⋅ψ\phi \cdot \psi in the symmetry group is equal to the composition ϕ∘ψ\phi \circ \psi of their individual underlying maps.

theorem

The underlying map of the inverse symmetry ϕ−1\phi^{-1} is the inverse of the map of ϕ\phi

Let EE be a real vector space equipped with a partial order and a unit element. For any symmetry ϕ∈Symmetry E\phi \in \text{Symmetry } E, the underlying unital positive linear map (channel) of the inverse symmetry ϕ−1\phi^{-1} is equal to the inverse channel of ϕ\phi.

instance

Symmetry group of EE

The set of order-automorphisms Symmetry E\text{Symmetry } E of a real ordered vector space EE with unit element 11 forms a group. In this group, the multiplication of two symmetries ϕ\phi and ψ\psi is defined as their composition ϕ∘ψ\phi \circ \psi, the identity element is the identity map idE\text{id}_E, and the inverse of a symmetry ϕ\phi is its inverse order-automorphism ϕ−1\phi^{-1}.

definition

Group isomorphism Symmetry E≅(E→p1[R]E)×\text{Symmetry } E \cong (E \to_{p1} [ℝ] E)^\times

For a real ordered vector space with unit EE, there is a group isomorphism between the group of symmetries Symmetry E\text{Symmetry } E and the group of units (E→p1[R]E)×(E \to_{p1} [ℝ] E)^\times of the monoid of unital positive linear maps (channels) on EE. This equivalence maps each symmetry ϕ\phi to the unit whose underlying value is the channel ϕ\phi and whose inverse is the channel ϕ−1\phi^{-1}.

instance

Group action of Symmetry E\text{Symmetry } E on the state space S(E)\mathcal{S}(E) via ϕ⋅ω=ω∘ϕ−1\phi \cdot \omega = \omega \circ \phi^{-1}

The group of symmetries Symmetry E\text{Symmetry } E acts on the state space S(E)\mathcal{S}(E) (denoted as S[R,E]\mathcal{S}[\mathbb{R}, E]). For a symmetry ϕ∈Symmetry E\phi \in \text{Symmetry } E and a state ω∈S(E)\omega \in \mathcal{S}(E), the action is defined by ϕ⋅ω=ω∘ϕ−1\phi \cdot \omega = \omega \circ \phi^{-1}, where ϕ−1\phi^{-1} is the inverse order-automorphism. This corresponds to the Schrödinger-picture pushforward of a state, where the state is transported by pulling it back along the inverse of the symmetry transformation.

theorem

Action of symmetry ϕ\phi on state ω\omega is ϕ⋅ω=ω∘ϕ−1\phi \cdot \omega = \omega \circ \phi^{-1}

Let EE be a real ordered vector space with a unit element. For any symmetry ϕ∈Symmetry E\phi \in \text{Symmetry } E and any state ω∈S(E)\omega \in \mathcal{S}(E), the group action of ϕ\phi on ω\omega is defined by the composition ϕ⋅ω=ω∘ϕ−1\phi \cdot \omega = \omega \circ \phi^{-1}, where ϕ−1\phi^{-1} is the inverse order-automorphism of ϕ\phi.

definition

Group action of GG on the state space S(E)\mathcal{S}(E) induced by ρ:G→Symmetry E\rho : G \to \text{Symmetry } E

Let GG be a group and EE be a real ordered vector space with a unit element. Given a group homomorphism ρ:G→Symmetry E\rho : G \to \text{Symmetry } E that represents GG as a group of order-automorphisms of EE, the function `stateSMul` defines an action of GG on the state space S(E)\mathcal{S}(E). For any element g∈Gg \in G and state ω∈S(E)\omega \in \mathcal{S}(E), the action results in a new state given by g⋅ω=ρ(g)⋅ωg \cdot \omega = \rho(g) \cdot \omega. Following the definition of symmetry actions on states, this is equivalent to the composition ω∘(ρ(g))−1\omega \circ (\rho(g))^{-1}.

theorem

stateSMul ρ 1 ω=ω\text{stateSMul } \rho \, 1 \, \omega = \omega

Let GG be a group and EE be a real ordered vector space with a unit element. For any group homomorphism ρ:G→Symmetry E\rho : G \to \text{Symmetry } E and any state ω∈S(E)\omega \in \mathcal{S}(E), the action of the identity element 1∈G1 \in G on the state ω\omega satisfies: stateSMul ρ 1 ω=ω\text{stateSMul } \rho \, 1 \, \omega = \omega where stateSMul\text{stateSMul} denotes the group action of GG on the state space S(E)\mathcal{S}(E) induced by ρ\rho.

theorem

(gh)⋅ω=g⋅(h⋅ω)(gh) \cdot \omega = g \cdot (h \cdot \omega) for the induced action on states

Let GG be a group and EE be a real ordered vector space with a unit element. Let ρ:G→Symmetry E\rho : G \to \text{Symmetry } E be a group homomorphism that represents GG as a group of order-automorphisms of EE. For any elements g,h∈Gg, h \in G and any state ω∈S(E)\omega \in \mathcal{S}(E), the action of the group on the state space satisfies the property (gh)⋅ω=g⋅(h⋅ω)(gh) \cdot \omega = g \cdot (h \cdot \omega), where the action g⋅ωg \cdot \omega is defined by `stateSMul ρ g ω`.

instance

Coercion of `OneParameterAutomorphismGroup` to R→(E→p1[R]E)\mathbb{R} \to (E \to_{p1}[\mathbb{R}] E)

This instance defines a coercion from the type of one-parameter automorphism groups `OneParameterAutomorphismGroup E` to a function type. It allows an element α\alpha representing a one-parameter family of symmetries to be treated as a mapping that takes a real number t∈Rt \in \mathbb{R} and returns a unital positive linear map (channel) α(t):E→p1[R]E\alpha(t) : E \to_{p1}[\mathbb{R}] E.

theorem

α(0)=id\alpha(0) = \text{id} for one-parameter automorphism groups

For any one-parameter automorphism group α\alpha on a system EE, the transformation corresponding to the parameter 00 is the identity map on EE, denoted as α(0)=idE\alpha(0) = \text{id}_E.

theorem

α(s+t)=α(s)∘α(t)\alpha(s + t) = \alpha(s) \circ \alpha(t) for one-parameter automorphism groups

Let EE be a system (represented as an order-unit space or effect algebra) and let α\alpha be a one-parameter automorphism group on EE. For any real numbers ss and tt, the automorphism associated with the sum s+ts + t is the composition of the automorphisms associated with ss and tt: α(s+t)=α(s)∘α(t)\alpha(s + t) = \alpha(s) \circ \alpha(t)

theorem

α(t)\alpha(t) is an Order-Automorphism with Inverse α(−t)\alpha(-t)

Given a one-parameter automorphism group α\alpha on a space EE (such as an effect algebra or order-unit space), for every t∈Rt \in \mathbb{R}, the map α(t)\alpha(t) is an order-automorphism. This means α(t)\alpha(t) is a unital positive linear map with a two-sided inverse that is also a unital positive linear map. Specifically, the inverse of α(t)\alpha(t) is given by α(−t)\alpha(-t), representing the physical intuition that running time backwards undoes the transformation.

definition

One-parameter automorphism group as a group homomorphism R→∗Symmetry E\mathbb{R} \to^* \text{Symmetry } E

Let EE be a real ordered vector space with a unit element. A one-parameter automorphism group α\alpha on EE is organized into a group homomorphism from the additive group of real numbers (R,+)(\mathbb{R}, +) (represented as `Multiplicative ℝ`) to the group of symmetries Symmetry E\text{Symmetry } E. This map associates each t∈Rt \in \mathbb{R} with the order-automorphism α(t)\alpha(t), satisfying α(0)=idE\alpha(0) = \text{id}_E and α(s+t)=α(s)∘α(t)\alpha(s + t) = \alpha(s) \circ \alpha(t). This formulation allows the dynamics to be treated as a general group action on the state space of the system.

definition

State evolution induced by a one-parameter automorphism group α(t)\alpha(t)

Let EE be a real ordered vector space with a unit element, and let S(E)\mathcal{S}(E) denote its state space (the set of unital positive linear maps from EE to R\mathbb{R}). Given a one-parameter automorphism group α\alpha on EE and an initial state ω∈S(E)\omega \in \mathcal{S}(E), the function `stateEvolution` defines the state at time t∈Rt \in \mathbb{R}. It is calculated as the action of the symmetry α(t)\alpha(t) on the state ω\omega, which is equivalent to the precomposition ω∘α(−t)\omega \circ \alpha(-t). This evolution satisfies the group action properties: α.stateEvolution(0,ω)=ω\alpha.\text{stateEvolution}(0, \omega) = \omega and α.stateEvolution(s+t,ω)=α.stateEvolution(s,α.stateEvolution(t,ω))\alpha.\text{stateEvolution}(s + t, \omega) = \alpha.\text{stateEvolution}(s, \alpha.\text{stateEvolution}(t, \omega)).

theorem

α.stateEvolution(0,ω)=ω\alpha.\text{stateEvolution}(0, \omega) = \omega

Let EE be a real ordered vector space with a unit element, and let S(E)\mathcal{S}(E) be its state space. For any one-parameter automorphism group α\alpha on EE and any initial state ω∈S(E)\omega \in \mathcal{S}(E), the state evolution at time t=0t = 0 is the identity, such that α.stateEvolution(0,ω)=ω\alpha.\text{stateEvolution}(0, \omega) = \omega.

theorem

α.stateEvolution(s+t,ω)=α.stateEvolution(s,α.stateEvolution(t,ω))\alpha.\text{stateEvolution}(s + t, \omega) = \alpha.\text{stateEvolution}(s, \alpha.\text{stateEvolution}(t, \omega))

Let EE be a real ordered vector space with a unit element, and let S(E)\mathcal{S}(E) denote its state space (the set of unital positive linear maps from EE to R\mathbb{R}). For any one-parameter automorphism group α\alpha on EE, any initial state ω∈S(E)\omega \in \mathcal{S}(E), and any time parameters s,t∈Rs, t \in \mathbb{R}, the state evolution satisfies the group property: α.stateEvolution(s+t,ω)=α.stateEvolution(s,α.stateEvolution(t,ω))\alpha.\text{stateEvolution}(s + t, \omega) = \alpha.\text{stateEvolution}(s, \alpha.\text{stateEvolution}(t, \omega))